Amphiphilic hydrolyzable polydimethylsiloxane-b-poly(ethyleneglycol methacrylate-co-trialkylsilyl methacrylate) block copolymers for marine coatings. I. Synthesis, hydrolysis and surface wettability

Amphiphilic hydrolyzable block copolymers composed of a poly(dimethylsiloxane) (PDMS) first block and a random poly(ethyleneglycol methacrylate (PEGMA)-co-trialkylsilyl methacrylate (TRSiMA, R = butyl, isopropyl) second block were synthesized by RAFT polymerization and dispersed as surface-active amphiphilic additives in a condensation cure PDMS matrix. Poly(tributylsilyl methacrylate) (pTBSiMA) and poly(triisopropylsilyl methacrylate) (pTiPSiMA) homopolymers and random copolymers PEGMA-co-TRSiMA were also synthesized as model polymers for comparison. The hydrolysis rates of the polymers in both ammonia buffer and artificial seawater were shown to drastically depend on the nature of the trialkylsilyl groups, with TiPSiMA polymers undergoing a slower rate hydrolysis. The incorporation of PEGMA units in the copolymers was found to increase the hydrolysis rate. On the other hand, the presence of the PDMS block led to a decrease in the hydrolysis rate for the block copolymers. Wettability studies of the elastomer PDMS-based films containing a surface-active additive block copolymer were carried out in both static and dynamic conditions. All the films were found to be both hydrophobic and lipophobic and became more hydrophilic after 30 days of water immersion. Measurements of advancing and receding contact angles with water confirmed the ability of the film surfaces to respond to the water environment.